Generally known projection objectives having variable focal lengths and used especially for images of the aforementioned type, as described, for example, in EP 058 651 B1 and U.S. Pat. No. 5,644,435, differ from each other essentially in the number of lenses, their arrangement and the technical construction data in connection with the conditions applicable to the optical system.
Since it is desirable for applications, in most cases, to vary the size and location of the image, thus adjusting the projection to the most diverse spatial dimensions, use is made mainly of zoom projection systems.
Therefore, projection objectives consist mainly of a zoom device, a compensating device and a focusing device of the type known from photographic lenses.
As a result in order to achieve a high image quality, such systems comprise many lens elements, are structurally very complex and, thus, very expensive. There is a need in the art for a simple, inexpensive projection objective including relatively few lens elements.